Pulp grinding machine having a tapered control roll

ABSTRACT

A log-grinding apparatus and process for making pulp including an improved process and log-grinding machine for compressing and releasing of pressure on the surface of a log in the presence of fluid to cause the natural lignin and resin fiber binders to be softened and dissolved whereby excellent wood fiber or pulp is formed and then readily separated from the log by a grinding roll. The log is rotatably driven through the machine lengthwise by the interaction of a group of angularly spaced rolls bearing upon the periphery of the log while liquid is applied to the log. The rollers engage the surface of the log at spaced points around the periphery thereof to apply pressure and squeeze fluid out of the log&#39;&#39;s surface and when pressure is released fluids are absorbed into the log&#39;&#39;s surface so that fluid is flushed in and out of the wood so that the fibers are thereafter easily separated from the log by the grinding roll that engages the log progressively from end-to-end.

United States Patent Bersano [54] PULP GRINDING MACHINE HAVING A TAPERED CONTROL ROLL [72] Inventor: Piero Bersano, Torino, Italy [73] Assignee: Norton Company, Worcester, Mass.

[22] Filed: Apr. 23, 1969 [21] Appl. No.: 818,602

Bersano, Piero A New Grinding Method, Tappi, Vol. 43 No. 1,Jan. 1960, p. 188A- 192A.

[ 1 Feb. 1, 1972 Primary Examiner-Reuben Friedman Assistant Examiner-Alfred DAndrea, Jr. Attorney-Allan R. Redrow [57] ABSTRACT A log-grinding apparatus and process for making pulp including an improved process and log-grinding machine for compressing and releasing of pressure on the surface of a log in the presence of fluid to cause the natural lignin and resin fiber binders to be softened and dissolved whereby excellent wood fiber or pulp is formed and then readily separated from the log by a grinding roll. The log is rotatably driven through the machine lengthwise by the interaction of a group of angularly spaced rolls bearing upon the periphery of the log while liquid is applied to the log. The rollers engage the surface of the log at spaced points around the periphery thereof to apply pressure and squeeze fluid out of the log's surface and when pressure is released fluids are absorbed into the log's surface so that fluid is flushed in and out of the wood so that the fibers are thereafter easily separated from the log by the grinding roll that engages the log progressively from end-to-end.

13 Claims, 5 Drawing Figures PULP GRINDING MACHINE HAVING A TAPERED CONTROL ROLL BACKGROUND OF THE INVENTION The field of invention is that of producing wood pulp from logs. It relates to a process for pulping in a centerless-type machine having rolls that support, rotate, compress and force feed logs lengthwise by a peripheral-type roll having a special burr pattern which effects loosening and separation of the individual fibers from the peripheral surface of the log. The fibers are first loosened by continuously flooding the log with a liquid while compressing and releasing the pressure on the peripheral portions of the log which causes the fluid to flush in and out of the wood substance.

The action of a centerless grinder to engage the periphery of an elongated object in a cluster of grinding wheels is well known in the prior art as shown in the U.S. Pat. No. l,579,933 to Heim. The machine includes an arrangement of guide means, a control wheel and an abrasive grinding wheel to simultaneously rotate and feed the elongated object to be worked upon, past the grinding station. The grinding wheel rotates rapidly while the control wheel is driven at a relatively much slower speed to produce a desired rate of rotation of the object exposed to the grinding wheel. The reaction of the object to the control wheel and grinding wheel forces, effects a positive feeding thereof past the grinding wheel. As the elongated object moves lengthwise past the grinding station it is cut down to a predetermined cylindrical size depending upon the spacing of the wheels. The elongated object is positively fed past the grinding station in response to the relative angular relationship of the grinding wheel and the control wheel and the rate of feed of course controls the degree of pressure created between the grinding wheel and the object being ground. These relationships and the procedures for operating such a machine following machine shop practices are well known.

This invention adapts the centerless grinder principle to the grinding of logs and the fiber separation principle disclosed in Bersano U.S. Pat. No. 3,255,070 to produce wood pulp and it has been discovered that an excellent quality of wood pulp can be produced from either fresh cut or dry logs provided certain angular relationships are maintained between the log and rolls and a proper surface is maintained on the roll that functions as the grinding wheel. In this connection, for the purpose of making wood pulp, in view of the very high pressure involved, a steel roll having a suitable surface configuration formed thereon is used instead of a true abrasive grinding wheel such as is used in a conventional centerless grinder and the apparatus shown in U.S. Pat. No. 3,255,070.

SUMMARY OF THE INVENTION Basically the present machine takes the form ofa cluster of rolls that cooperate with the log in substantially the manner of the grinding wheel, regulating wheel and work support of the centerless grinding acting upon a rod to be ground to a given cylindrical size. The apparatus here disclosed includes a particular angular relationship of the rolls to the log to effect longitudinal feeding of the log through the machine while at the same time effecting a quite efficient fiber separation from the log. The speed of rotation of the log, the working pressure of the fiber-separating roll and the speed of longitudinal feed of the log through the machine can be precisely controlled by the relationship of the angles at which the rolls are disposed with respect to the log and by controlling the speed at which they are driven. Suitable drive means are associated with the rolls to positively rotate them at their respective design speeds to accomplish the desired rotation, grinding pressure and feeding of the log. One of the rolls is driven rather slowly to act as a feed control roll following the terminology of the centerless grinder art, and another grinding roll is driven more rapidly to effect fiber separation from the log to roughly simulate the grinding wheel function of a centerless grinder. Another support roll, that may be an idler roll, is also disposed in the cluster of rolls to act as a support for the log and serve the function of assisting in compressing the surface of the log when it comes in rolling contact therewith. The feed control roll and rapidly driven grinding roll also cooperate with the surface of the log to effect additional compression and release actions at spaced points around the periphery of the log. The action of each of the idler and control rolls is to each produce a single step of relatively high degree of pressure to be applied against the logs surface along the line of each rolls contact with the log during each revolution of the log to squeeze the fluids out of the logs surface so that upon the release of compression, the fluids are caused to penetrate deeply into the wood surface. The rapidly driven grinding roll is provided with a surface configuration that engages the logs surface to produce a multiplicity of rapid vibratory compression cycles against the surface of the log during each revolution to cause the fibers to separate from the logs surface as will appear more fully in the detailed portion of the specification which follows.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a plan view of the apparatus taken on line 1-1 of FIG. 2, showing the preferred form of the invention;

FIG. 2 is a view taken on line 22 of FIG. 1, showing in addition, the paths of travel of two logs through two different stations for fiber separation;

FIG. 3 is a view taken on line 3-3 of FIG. 1;

FIG. 4 is a diagrammatic view showing the relationship of the logs to the several rollers at the two grinding stations; and

FIG. 5 is a detail view of the preferred surface configuration of the fiber separating or grinding roll of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings the machine includes a grinding roll 10 which effects fiber separation from the log and a feed control roll 11 which determines the rate of log rotation, both of which are driven. The grinding roll is preferably powered by an electric motor 12 through a drive connection, which motor may be as large as 250 hp. or larger and is driven to rotate the grinding roll at speeds in the range 3,600 r.p.m. and higher. The control roll is driven by a much smaller motor 13 through a variable speed driven mechanism 14 and suitable angular drive means 15 to rotate the control roll at about 50 r.p.m. The r.p.m. of the control roll 11 is adjustable within a range of from 9 to 54 r.p.m. to control the speed of rotation of the log as will appear more fully below. The cluster of roll which completes the basic machine elements includes an idler roll 16 spaced from the other two rolls as best shown in FIG. 4, to complete the confined passage of diminishing size for the log and which forces the log to be pressed against the grinding roll and control roll as the log is positively fed through the machine by the interaction of the log with rolls I0, 11 and 16.

Suitable frame means including vertical columns 17 and horizontal beams 18 and 19 are provided to support bearings for the respective rolls. The motors l2 and 13 are suitably supported relative to the frame to deliver the required power to the respective driven rolls. The grinding roll is mounted to rotate in a fixed position in the frame. The idler roll 16 and control roll 11 are adjustably supported from the frame and such adjustment is provided so that their respective bearings 20 and 21 and 22 and 23 respectively may be suitably positioned whereby the desired angular relation of their peripheries may be established.

Shower means to produce a line of fluid showers 24 and 25, are provided to spray the necessary fluids over the periphery of the grinding roll and for wetting the surface of the log being ground so that the compression and release method of separating wood fibers from the log can be performed. This basic fiber separation method is disclosed in the above-mentioned prior U.S. Pat. No. 3,355,070 granted June 7, 1966. This invention provides an improvement on the method and apparatus there disclosed and optimizes the fiber separation process to produce better quality pulp with more efficient utilization of energy. Further the adaption of the centerless grinder principle makes possible the building of a machine for converting a log to pulp wherein a log of any diameter and length can be fed longitudinally through a grinding station to be reduced to pulp. If desired, this can be accomplished at a single grinding station like that described above, however, to make maximum use of the apparatus, it is preferable to provide several grinding positions spaced around the periphery of the grinding roll 10 and as best shown in FIG. 4 a second station is shown having a second control roll 26 that cooperates with a second idler roll 27 and grinding roll 10. The control roll 26, idler 27 and grinding roll 10 provide in effect a second cluster of rolls formed about a second passage of diminishing size for receiving another log or a log of relatively much smaller diameter for example one that has previously been ground in the first grinding station made up of rolls I0, I I and 16. The log passed through the second grinding station is further reduced in diameter in that station to produce additional pulp. Other stations could be built around the single driven grinding roll 10 if desired. As shown in FIG. 4, second shower means are provided to produce fluid sprays 28 and 29 which are directed against the surface of the grinding roll and log.

Referring to FIG. 1, it will be seen that the grinding roll 10 takes the form of a steel cylinder. The surface of the grinding roIl has a burr pattern thereon configured as shown in FIG. 5. The burr pattern comprises spaced rows of V-shaped grooves with teeth between the grooves spaced about the axis of the roll. The dimensions of these grooves and teeth which bear against the log are not critical but are preferably selected to be in the order of the size of the fibers being separated and the type of pulp desired. For example, the depth D of the groove shown in FIG. may be approximately 0.04 inch for poplar logs, the other dimensions of the teeth are in proportion. The surface pattern is produced in an equispaced design around the grinding roll and has a design such that when it rotates against the surface of the log the relative motion of the surface bearing on the log produces a continuous vibratory action that moves along the log's surface faster than the body of the log is moving past the grinding station to produce a separation of the loosened fibers from the surface of the log. Since there are many rows of teeth bearing against the logs surface as the log and grinding roll rotate together under pressure, there is produced a rapid beating and rubbing action that is repeated and then relieved with each tooths contact with the logs surface, to effect a rapid vibratory cycle with rapid pressure relief. This is believed to cause a frictional action within the softened fiber zone in the log to cause the fluid carried on the surface of the grinding roll and within the fiber mass to flush the fibers free. There appears to be a combined hydraulic action wherein fluid carried on the surface of roll is forced into the fiber layer as it and the log roll together and then the frictional action produces heat. In any event, whatever the action, the bulk of the fibers can be seen to tumble free of the log just at or in front of the line of tangency of the grinding roll contact with the log as the log surface rolls toward the grinding roll so that the bulk of the fibers fall free of the log without being trapped between the log and grinding roll, thereby minimizing the possibility of breaking the fibers of undue rubbing contact Referring to FIG. 3, as the grinding roll and log roll together, the previously softened fiber zone to the depth of about 1.5 to 2 mm. is stripped from the log along the entire line of contact between the log and the grinding roll. The fibers fall onto the pan or deflector 30 to be washed down into a suitable collecting pit under the machine.

The feed control roll I] and idler roll 16 cooperate in the fiber-softening process by effecting a relatively deep compression of the logs surface once during each revolution of the log to squeeze the fluids out of the log to wash out the resins and ligins that bond the fibers together. This compression is produced all along the lines of contact of the log with the control roll and idler roll and as these rolls have a generally smooth surface and are moving at the same speed as the logs surface, the action is that of a relatively low pressure cycle extending over a longer time period as compared with the contact action of the grinding wheel surface previously described. In comparison it may be said that the grinding roll provides a generally rapid vibratory and quickly relieved pressure contact with the log while the control roll and idler roll each provide a single pressure contact and relatively rather longer time period of contact with the logs surface during each revolution of the log. When the highly compressed log surface moves past the zone of contact with each of the idler and control rolls, the log's somewhat resilient surface expands to act like a sponge and suck in the fluids showered over its surface at these areas from spray 31 next to the idler roll and spray 32 next to the control roll. Similar shower means are used with such additional grinding stations as are built into the machine.

To effect the desired angular relationship between the several rolls forming cooperating cluster, the control roll 11 for example is designed to have a truncated conical shape with the smaller end of the truncated cone carried in bearing holder 22 at the infeed end of the machine or the right-hand side as shown in FIGS. 1 and 2. The larger end of control roll 11 is carried in bearing mounting 23 at the left end of the machine. The bearings mountings 22 and 23 are adjustably carried on the posts 17 for changing the relationship of the axis about which the control roll 11 rotates relative to the axis about which grinding roll 10 rotates in order to adjust the feed rate for delivery of the log though the machine. It is apparent that because of the positive feed principle of a centerless grinder action, any degree of grinding pressure can be established by changing the feed rate.

As indicated above it is preferred that a feed rate be established for the logs being ground to cause fiber removal for a depth of about 1.5 to 2 mm. Fibers and/or bundles of fibers have been successfully removed to a depth of 3 mm. but when the grinding pressure is increased to, in effect, remove fibers to a depth of 5 mm., there is an undue amount of fiber breakage and even burning of the wood caused by compressing the wood at too high a pressure so that apparently wood that has not been impregnated with the flushing fluids is worked to a charring temperature, causing fiber breakage and burning before the lignins and resins can be softened and removed. The breaking and charring of fibers degrades the quality of the resulting pulp.

The idler roll I6 which completes the cluster of rolls including rolls I0 and II, is also a truncated cone. As best seen in FIG. 2 it is mounted with its large end at the infeed end of the machine and with its small end at the exit end. The idler is cartied in the adjustable bearing carriers 20 and 21 and is positioned to have a line bearing contact on the log which is ground to have a conical periphery while passing through the grinding station passage formed by rolls 10, 11 and 16.

The second grinding station including control roll 26 and idler roll 27 are designed and mounted in the same manner as feed control roll 11 and idler roll 16 except for their smaller diameters which are provided as here shown for working on logs having a smaller diameter. When the second station is adapted to receive logs that have been passed through the first grinding station, the truncated conical rolls of the second station are preferably reversed in the direction of their mounting so that the infeed to the second station will be adjacent the exit from the first station. The working conditions in the second station may be adjusted independently of the first station to provide a proper grinding action on a log of smaller diameter in order to effect a proper compression and release cycling to remove fibers to a depth of preferably L5 to 2 mm.

The machine described above can be designed to take a log of any reasonable diameter. The length is immaterial. Once the geometry of the cluster of rolls has been set, regardless of the diameter of the log fed in, the same depth of fiber involvement is accomplished. A debarker can be provided immediately before the first grinding station or previously debarked logs may be fed immediately to the machine. In the case of dry wood it is preferred that it be given a preliminary soaking before delivery to the grinder but only a slight surface penetration of water is needed to begin softening of the surface fibers to minimize breakage thereof when the log first meets the rolls to provide water to flush in and out. After a few revolutions, the compress and release cycling will have started and from that point on all of the fibers are easily liberated by the grinding roll action.

As suggested above, it is believed the formation of elevated temperature in the surface layer of the wood is caused by the frictional action of the grinding roll surface bearing against the wood to cause frictional movement of wood on wood and passage in and out of fluid. It is therefore important that the fluid supplied at shower 25 and corresponding showers in any other grinding stations, be controlled to avoid cooling the grinding wheel too much which would prevent the formation of correct temperature within the wood. Preferably, the shower 25 is controlled to cool the surface of roll to hold it at a temperature to prevent the frictional heat developed from burning the wood. It is desired to also keep the surface of roll at a temperature below 100 C. to permit it to carry a film of fluid on its surface as it moves forwardly to meet the log in order to produce the hydraulic action mentioned above which assists in freeing the fibers from the surface of the log in an undamaged condition and before the fibers are trapped between the grinding wheel surface and the rest of the log. [t has also been noted that when the spray temperature control on the grinding roll is operated to maintain the 100 C. temperature that the water and steam action on the lignins and resins permits their being softened and dissolved without any noticeable conversion or discoloration ofthe lignins.

The apparatus above described has produced a pulp from dry ltalin poplar logs that was made into a standard hand sheet and tested by TAPPl standard tests and attained breaking length 2,000 meters, freeness 180, tear 27, and unbleached brightness of 42 GE. The pulp can be readily bleached to im prove its brightness as can be demonstrated by the addition of 3.5 percent peroxid or other bleaching agents.

The pulp coming from this machine will be found to be, in general, brighter because certain soluble matter has been washed out of the log by the compressing and release cycles before the fibers are liberated. There appears to be little or no reversion and if necessary the pulp can be bleached in a normal manner with hydrosulphite or peroxide.

The apparatus described above is adapted to receive logs from opposite sides of the machine, the right hand side in the top cluster of rolls 10, 11 and 16 as shown in FIGS. 1 and 2 and from the left hand side in the bottom cluster of rolls 10,26 and 27. As the log engages the control roll 16, idler 11 and grinding roll 10, the log begins to be rotatably fed by the control roll through the machine. The control roll determines the rate of rotation and the grinding roll is essentially operative to strip off the fibers. As above described the compression and release cycles performed in the presence offlushing fluid, conditions the fibers for easy separation from the log and the action of grinding roll 10 coupled with proper control of the temperature of the surface of the grinding wheel effects the desired fiber separation with a minimum of fiber damage and consumption of energy. The compression and release cycle is further controlled to effect a sponging fluid penetration into the logs surface with a relative high-pressure longer time cycle coupled with the use of a higher frequency shorter frictional bearing action of the grinding roll surface to raise the temperature of the flushing fluid within the log to soften the binding agents without degrading the ultimate pulp whereby provide an improved fiber liberation method.

The groove pattern on the grinding roll is designed to take into account the wood being ground and the amount of shower fluid used. The grinding roller, rubbing against the wood surface, produces friction which in turn produces steam from the fluid on the surfaces of the roller and wood. With softer woods the specific pressure between a given area of the roller and wood when in contact, is not so great and the heat generated by the friction is limited as the grinding roller tube rubs on the wood and the grooves and amount of shower fluid must be designed so that too much water or shower fluid is not delivered into the grinding zone, in order to avoid cooling the roller and wood so much that steam is not produced. In the case of grinding woods that are harder, the degree of specific pressure in a given area that is produced between the roller and wood surface is higher and more frictional heat is generated. The shape of the groove pattern and shower controls are adjusted to cause more water to be carried into the grinding zone when compared to the grinding of softer woods.

It will be obvious to those skilled in the art that many modifications of the invention disclosed herein, may be made. The machine readily suggests itself for adaption to a portable form including a gasoline powered generator for use in the forest. This has the advantage that the bark stripped from the logs and other chemicals washed from the log during fiber separation, can be left on the spot for better growth of future stands of timber. This and such other modifications as may occur to others are to be comprehended within the scope of the following claims.

What is claimed is:

1. A machine for grinding a log into wood pulp comprising:

a frame;

a grinding roll mounted to be rotatably driven about an axis on the frame and the roll having a burr pattern on its peripheral surface for producing vibrations, friction and removing wood fibers from the log;

a control roll, mounted to be rotatably driven about another axis on the frame, spaced from the grinding roll for sim ultaneously engaging, compressing, rotating and feeding the log lengthwise between the grinding and control rolls;

the axis of said control roll being inclined at a small angle relative to the axis of the grinding roll;

an idler roll, rotatably mounted on the frame, spaced from the grinding and control rolls for engaging, compressing, forcing and maintaining the log against the grinding and control rolls, the grinding, control and idler rolls being arranged relative to each other so each roll has line contact with the log, produce areas of compression and decompression in the log and form between themselves a passage of diminishing size through which the log is rotatably fed from a larger entrance to the passage by the control roll and reduced in size by the grinding roll as it passes to a smaller exit from the passage;

said control roll having a peripheral surface tapering from a small end at the entrance end of said passage toward a large end at the exit end of the passage;

means for rotating the control and grinding rolls; and

means for showering the log and impregnating the areas of decompression with a fluid to loosen the wood fibers prior to their being removed from the log by the grinding roll.

2. A machine according to claim 1 wherein the idler roll rotates about an axis inclined at an angle less than the small angle of the control roll relative to the axis of rotation of the grinding roll.

3. A machine according to claim 2 wherein the idler roll has a peripheral surface tapering from a large end at the entrance end of the passage toward a small end at the exit end of the passage.

4. A machine according to claim 1 wherein the grinding roll is cylindrical about its axis of rotation and has rows of spiraling grooves and teeth between the grooves on its cylindrical peripheral surface.

5. A machine according to claim 1 having drive means to rotate the grinding roll more rapidly than the control roll.

6. A machine according to claim 5 which further comprises:

a second control roll, rotatably mounted on the frame, spaced from the first and said control roll and grinding roll for engaging, compressing, forcing, rotating and feeding a second log lengthwise between the grinding and second control rolls;

a second idler roll, rotatably mounted on the frame, spaced from the grinding and second control rolls for engaging, compressing, forcing and maintaining the second log against the grinding and second control rolls, the grinding, second control and second idler rolls being arranged relative to each other so each has line contact with the second log, produce areas of compression and decompression in the second log, and forming between them a second passage of diminishing size having an entrance end and exit end through which the second log is rotatably fed by the second control roll and reduced in size by the grinding roll, said second control roll having a peripheral surface tapering from a small end at the entrance end of said passage toward a large end at the exit end of the passage; and

means for rotating the second control roll more slowly than the grinding roll; and means for showering the log and impregnating the areas of decompression of the second log with a fluid to loosen the wood fibers prior to their being removed from the second log by the grinding roll.

7. A machine according to claim 6 wherein the second control roll rotates about an axis inclined relative to the axis of rotation of the grinding roll and has a peripheral surface tapering from a small end at an entrance end of the second passage toward a large end at an exit end of the second passage.

8. A machine according to claim 7 wherein the second idler roll rotates about an axis inclined relative to the axis of rotation of the grinding roll.

9. A machine according to claim 6 wherein the passages are of different average cross-sectional size, said second passage size being smaller than said other passage to receive the log exiting from the other passage to further loosen fibers from the surface of the log.

10. A machine according to claim 9 wherein the entrance ends to each of the passages is larger than their exits ends and are at opposite sides of the machine whereby the logs fed through the respective passages move therethrough in opposite directions.

11. A machine according to ciaim 1 wherein the grinding roll has a cylindrical shape and rows of grooves and teeth disposed in a pattern on its peripheral surface wherein the grooves are parallel to the axis of the roll.

12. A machine according to claim 1 wherein the idler roll rotates about an axis inclined at a small angle relative to the axis of the grinding roll and the direction of the inclination of the idler axis being opposite to the direction of inclination of the control roll axis relative to said grinding wheel axis whereby the difference in angle of inclination between the idler roll axis and the control roll axis is equal to the addition of their angles of inclination.

13. A claim according to claim 12 wherein the idler roll has a peripheral surface tapering from a large end at the entrance of the passage toward a small end at the exit end of the passage. 

1. A machine for grinding a log into wood pulp comprising: a frame; a grinding roll mounted to be rotatably driven about an axis on the frame and the roll having a burr pattern on its peripheral surface for producing vibrations, friction and removing wood fibers from the log; a control roll, mounted to be rotatably driven about another axis on the frame, spaced from the grinding roll for simultaneously engaging, compressing, rotating and feeding the log lengthwise between the grinding and control rolls; the axis of said control roll being inclined at a small angle relative to the axis of the grinding roll; an idler roll, rotatably mounted on the frame, spaced from the grinding and control rolls for engaging, compressing, forcing and maintaining the log against the grinding and control rolls, the grinding, control and idler rolls being arranged relative to each other so each roll has line contact with the log, produce areas of compression and decompression in the log and form between themselves a passage of diminishing size through which the log is rotatably fed from a larger entrance to the passage by the control roll and reduced in size by the grinding roll as it passes to a smaller exit from the passage; said control roll having a peripheral surface tapering from a small end at the entrance end of said passage toward a large end at the exit end of the passage; means for rotating the control and grinding rolls; and means for showering the log and impregnating the areas of decompression with a fluid to loosen the wood fibers prior to their being removed from the log by the grinding roll.
 2. A machine according to claim 1 wherein the idler roll rotates about an axis inclined at an angle less than the small angle of the control roll relative to the axis of rotation of the grinding roll.
 3. A machine according to claim 2 wherein the idler roll has a peripheral surface tapering from a large end at the entrance end of the passage toward a small end at the exit end of the passage.
 4. A machine according to claim 1 wherein the grinding roll is cylindrical about its axis of rotation and has rows of spiraling grooves and teeth between the grooves on its cylindrical peripheral surface.
 5. A machine according to claim 1 having drive means to rotate the grinding roll more rapidly than the control roll.
 6. A machine according to claim 5 which further comprises: a second control roll, rotatably mounted on the frame, spaced from the first and said control roll and grinding roll for engaging, compressing, forcing, rotating and feeding a second log lengthwise between the grinding and second control rolls; a second idler roll, rotatably mounted on the frame, spaced from the grinding and second control rolls for engaging, compressing, forcing and maintaining the second log against the grinding and second control rolls, the grinding, second control and second idler rolls being arranged relative to each other so each has line contact with the second log, produce areas of compression and decompression in the second log, and forming between them a second passage of diminishing size having an entrance end and exit end through which the second log is rotatably fed by the second control roll and reduced in size by the grinding roll, said second control roll having a peripheral surface tapering from a small end at the entrance end of saiD passage toward a large end at the exit end of the passage; and means for rotating the second control roll more slowly than the grinding roll; and means for showering the log and impregnating the areas of decompression of the second log with a fluid to loosen the wood fibers prior to their being removed from the second log by the grinding roll.
 7. A machine according to claim 6 wherein the second control roll rotates about an axis inclined relative to the axis of rotation of the grinding roll and has a peripheral surface tapering from a small end at an entrance end of the second passage toward a large end at an exit end of the second passage.
 8. A machine according to claim 7 wherein the second idler roll rotates about an axis inclined relative to the axis of rotation of the grinding roll.
 9. A machine according to claim 6 wherein the passages are of different average cross-sectional size, said second passage size being smaller than said other passage to receive the log exiting from the other passage to further loosen fibers from the surface of the log.
 10. A machine according to claim 9 wherein the entrance ends to each of the passages is larger than their exits ends and are at opposite sides of the machine whereby the logs fed through the respective passages move therethrough in opposite directions.
 11. A machine according to claim 1 wherein the grinding roll has a cylindrical shape and rows of grooves and teeth disposed in a pattern on its peripheral surface wherein the grooves are parallel to the axis of the roll.
 12. A machine according to claim 1 wherein the idler roll rotates about an axis inclined at a small angle relative to the axis of the grinding roll and the direction of the inclination of the idler axis being opposite to the direction of inclination of the control roll axis relative to said grinding wheel axis whereby the difference in angle of inclination between the idler roll axis and the control roll axis is equal to the addition of their angles of inclination.
 13. A claim according to claim 12 wherein the idler roll has a peripheral surface tapering from a large end at the entrance of the passage toward a small end at the exit end of the passage. 